He's My Fiancée ! : I Went Back To The Past and You ! - Chapter 400 - 401: Once Upon a Building-II

The world was once at war with 10 alternate worlds. This was known as the Concept War and our world won 60 years ago. All of this was concealed so no normal people are aware of this fact in the current time.

After the death of his grandfather, the high-school student Sayama Mikoto is suddenly summoned by the giant corporation IAI. He learns this world is headed for destruction due to the acceleration of the Minus Concepts. To prevent this, negotiations must be undertaken with the survivors of the other parallel worlds so their 10 concepts can be released.

And so Sayama is caught up in the final battle to clean up after the Concept War which left behind so much enmity.

She was stupidly in love with him. Because of him, she became rude and unreasonable, overbearing, jealous, insane. But he did not spare a glance to her. Married for two years, he didn’t favor her once, letting her become the laughing stock of the whole world. Eventually, she ended up in an affair, leading to her tragic death.

I am serious about saving people, I am professional in protecting people, and I like hunting for treasures. . . .

Emergency doctor Lu Fei was forced to travel to a small town in the United States in a parallel universe, got the rescue system, and became a legal mercenary by chance.

As a real man, you must always cut open people’s bodies to save people from danger; you must often fight and kill, and use thunderbolt methods with compassion!

- Description from novelbuddy

There are always four kinds of people in the traditional Mary Sue world. The Male Lead, the Mary Sue female lead, the woman who never wanted to see the female protagonist live a good life, and the infatuated man willing to destroy heaven and earth to get the female lead.